1. Field of the Invention
The present invention relates to a contradeglutitious solid herbicidal composition (i.e., a herbicidal composition not easy to swallow). More specifically, it relates to a contradeglutitious solid herbicidal composition containing, as a herbicidal agent, a "1,1'-dimethyl-4,4'-bipyridylium" salt (i.e., so-called "paraquat" salt), which is not easily swallowed even if such a paraquat salt solution is accidentally or intentionally drunk. The term "paraquat" used herein means 1,1'-dimethyl-4,4'-bipyridinium cation.
2. Description of the Related Art
The importance of herbicides or pesticides in modern agriculture is widely recognized and many herbicides or pesticides are in practical use. Herbicides or pesticides practically used must be registered, after being subjected to a severe examination including the toxicity and safety thereof based on the laws and regulations concerned. Accordingly, as long as herbicides or pesticides are properly used according to instructions for use, they will not harm the human body in any way. However, the present status is such that toxic or poisonous accidents caused by a portion of herbicides or pesticides still occur in spite of the fact that the proper handling of herbicides or pesticides and the preventing of injury thereby to the human body has been taught and the dangers of improper usage have been widely announced for a long time. In particular, a herbicide, a paraquat salt, is widely used because of the strong herbicidal effect and easy applicability thereof, and quite a large number of toxic or poisonous accidents have been caused by the accidental or intentional drinking of the paraquat salt despite clear indications of its toxicity. This is because paraquat has very strong acute toxicity and is commercially available in the form of an aqueous solution having a relatively high concentration.
Paraquat is generally marketed as an about 24 W/V % aqueous paraquat dichloride solution. When used, the raw paraquat solution is diluted 300 to 1500 times with water and the resultant diluted paraquat solution is generally sprayed as a weed-killer in an amount of 100 to 150 liters per 10 are (i.e., 100 m.sup.2). The oral acute toxicity of paraquat dichloride is an LD.sub.50 of 166 to 217 mg/kg (rat) and it is reported in "Kyukyu Igaku" 4(4), p 399 (1980) that the lethal dose of paraquat for humans is approximately 15 ml of the 20% aqueous paraquat solution (i.e., approximately 3 g of paraquat). On the other hand, it is reported in "Gekkan Yakuji" 25(8), p 147 (1983) that an average amount drunk in one mouthful by an adult human is generally approximately 40 ml. This means that, if a commercially available paraquat solution is accidentally or intentionally drunk, a mouthful of the paraquat solution is sufficient to be lethal to a human.
Various attempts have been made to prevent accidental toxic or poisonous injury caused by paraquat. For example, odorants or colorants are mixed into the paraquat solutions to prevent accidental drinking by giving it an unpleasant odor or color. However, this is not effective for infants or against intentional drinking. Furthermore, the inclusion of nauseants in the paraquat solutions has been proposed, to rapidly remove the mistakenly drunk paraquat from the stomach and other digestive system prior to the absorbance of paraquat into the body therethrough. However, it is extremely unfortunate that, at present, once paraquat is swallowed, a reliable and effective curing or treatment method is not available, although this depends upon the amount swallowed, even if the paraquat is vomitted at an early stage.
Consequently, although various attempts have been made to solve the above-mentioned problems, an appropriate and effective means has not, as yet, been found. In order to prevent toxic or poisonous accidents caused by the oral intake of paraquat, it is thought that the concentration of commercially available paraquat should be decreased so that a lethal amount is not reached unless a relatively large amount of a paraquat solution is drunk. However, this causes disadvantages in the transportation and storage of paraquat solutions and also impairs the inherent easy handling characteristics of paraquat. On the other hand, it is considered that, when paraquat is marketed in the form of a solid instead of an aqueous solution, the paraquat becomes difficult to drink, toxic or poisonous injuries caused by the accidental intake of paraquat can be prevented, and, furthermore, the transportation and storage thereof are convenient. However, since paraquat is completely soluble in water, an aqueous solution containing a lethal amount of paraquat is easily prepared from such solid paraquat by the addition of, for example, a mouthful of water, and thus it is practically impossible to prevent a person with suicidal intent from taking the poison.